This invention relates to a novel polyurethane composition characterized by excellent transparency, hardness, and stain and scratch resistance, which is particularly suitable for such applications as no-wax floor finishes end for single glass sheet safety glass constructions. The ever-growing energy crisis has imposed on automobile manufacturers the obligation to reduce automobile weight in order to improve fuel economy. As one of small but significant contributions to the weight reduction, it has been proposed to replace the conventional automobile safety glass, presently made of two glass sheets held together by a clear plastic interlayer, by a single glass sheet backed by a transparent synthetic polymer layer, such as plasticized polyvinyl butyral or a polyurethane, to improve impact resistance.
While use of polyurethane compositions both in floor finishes and in safety glass construction is known, it has always been difficult to combine in one product good stain and scratch resistance since those properties are generally considered to be incompatible with each other. It thus is desirable to provide polyurethane compositions having a good balance of properties, including good stain and scratch resistance.
U.S. Pat. No. 3,979,548 to Schafer et al. describes a polyurethane composition suitable as a scratch-resistant coating on the interior surface of automobile safety glass. In order to preserve the desirable physical properties of the cured polyurethane during bonding at an elevated temperature, nonstoichiometric amounts of the polyol component and the polyisocyanate component are used, the proportion of the former being larger than calculated.